XAS studies are proposed for the trinuclear sites present in the multicopper oxidases. The fully reduced, fully oxidized and oxygen intermediate forms of native and type 1 mercury substituted laccase (Lc) will be investigated by EXAFS to probe for possible metal-metal interactions which would indicate oxygen bridging at the trinuclear site and to determine if a short Cu-O interaction is present in the first shell data on the intermediates. We will quantify the amount of Cu(I) present in both intermediates using the Cu K-edge structure. Peroxide and azide bound forms of T1Hg Lc, native Lc, and ascorbate oxidase (AO) will also be systematically studied by EXAFS and X-ray absorption edge methods to correlate spectroscopic results with crystallographic data on ligand bound forms of AO. These experiments are of critical importance in developing an understanding of the role of the trinuclear site in the four electron reduction of dioxygen to water. Finally XAS studies will be directed to ceruloplasmin (Cp) to probe the oxidation state of the coppers in the unusual (i.e. EPR nondetectable) trinuclear copper cluster which appears to be present in the resting form of this enzyme in rapid preparations and to elucidate the possible interactions among the trinuclear coppers as compared with other multicopper oxidases.